With more stringent environmental legislation, waterborne coatings are replacing solvent borne coatings. The components in these waterborne coatings are typically anionic vinyl or acrylic polymers and pigment dispersions. Unfortunately, the carboxylate chemical groups and surfactants that allow aqueous solubility or dispersability can also lead to undesirable water sensitivity of the dried coating.
Carboxylated graft and block acrylic copolymer dispersions have better aqueous coalescence stability compared to those with a linear random copolymer of the same molecular weight, polarity, and acid number. The carboxylated graft and block acrylic copolymers also provide superior aqueous flocculation stability of pigment dispersions compared to a linear random acrylic copolymer of the same acid number.
Coating solutions comprising structured carboxylated acrylic polymer dispersions or emulsions and pigment dispersants have high solids at usable viscosities with greater stability than those made with random linear carboxylated copolymers with the same acid number. The lower acid content, and removal of the need for low molecular weight surfactants, also improves the moisture sensitivity of the dried coating.
In spite of the benefits imparted by these carboxylated structured acrylic polymers to aqueous solution stability, the hydrophilic carboxylate groups still remain behind in the coating and can cause problems with moisture sensitivity. Thus, there is still a need for further improvement in moisture resistance of the dried coating.